Aircraft: A320
Phase of flight: taxi
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Weight And Balance

In preparation for our flight; I noticed our planned takeoff weight was roughly 164;500 lbs. Knowing that planned weight was near our maximum takeoff weight; I requested performance numbers for Runway 28L and Runway 1R at an assumed weight of 166;000 lbs. The performance numbers came back for Flex takeoff setting of Flaps 1 for 28L and a Flex takeoff setting of Flaps 3 for Runway 1R. The Captain and I discussed the benefits of both runways and the decision was made to disregard the Runway 28L numbers. With that; a Flex takeoff with Flap 3 for 1R was entered into the FMGC. While taxing and knowing we were to fly the Porte departure from the 1's; the Captain asked me to retrieve the performance numbers for Runway 1L. While waiting for the Takeoff data; the Captain and I both shared our skepticism about the aircraft performance abilities for 1L. We were both surprised to see that Flaps 3 performance numbers came up for 1L with the Final Weight data of roughly 164;000 lbs. We were even more surprised to see that TOGA thrust was not necessary. So I proceeded to the box and made the appropriate changes to the runway. Switched from 1R to 1L; entered the V speeds for Flaps 3 at 1L; entered the Flex temperature for 1L and somewhere in there I mistakenly changed the current flap setting of 3 to the erroneous setting of 1. No adjustment to the actual flaps was necessary due to Flaps 3 was planned for Runway 1R. Shortly there after we commenced with the Before Takeoff Checklist. With his hand on the Flap handle Captain questioned the flap setting. I glanced down behind the flap handle where the Takeoff data was located and inadvertently confirmed Flaps 1. I can only assume I failed to look at the appropriate runway data. We proceeded to Line Up and Wait on runway 1L. The Captain transferred the controls over to me. Once cleared for takeoff; I applied the power appropriately considering the weight of the aircraft and the length of the runway. Acceleration felt normal. The 'V1' and 'Rotate' call out came prior to crossing Runway 28L which; on reflection; did stand out as I began a slower than normal rotation. In the Second Segment Climb the aircraft accelerated as well as I expected for a heavy A320. Crossing the acceleration altitude I lowered the nose; saw a positive green trend arrow; brought throttles back to Climb and called for flaps 1. That is the moment I realized I failed to keep situation awareness on the ground and that led to an Undesired Aircraft State. We were very fortunate that we did not experience an engine failure after V1. Why did we takeoff in an undesired aircraft state? Not because the First Officer made a mistake; but because at no time did I double check the takeoff data for 1L with my own eyes nor did I confirm that the data was properly loaded into the FMC. I had simply watched the data being loaded thinking that I was verifying it at the same time. Complacency on my part certainly played a major role in my actions. In retrospect; I recognize that although virtually every single pilot on the Airbus has many years of experience on it; mistakes will still occur. We need to be cognizant of complacency; remember our SOPs; and be always vigilant in order to back each other up thus ensuring the double checking and crosschecking required for the safe operation of our aircraft. An A320 departed SFO Runway 1L with Flaps 1; Flex power near maximum gross takeoff weight and they realized after takeoff that the slow climb and acceleration were the result of not having selected Flaps 3.